White Spot on Brand New Car

Bought a 2017 Honda Accord Sport SE back in November. After having the car a few days noticed white spots on the passenger seat. (I will attach picture). We contacted the dealership and took it in twice to have them try and remove the spots/stains, but were unable to do so. Does anyone know what this might be and how to remove it? When you try to clean it with something it appears as if it has gone away only to come back a few hours later.